This project involves the use of psychophysical tets to study cone function in individuals with color vision defects, with special emphasis on acquired deficiencies. First, a saturation discrimination task is used to determine the hue sensitivity of normal volunteers and patients with abnormal color vision. Second, we are examining whether we can specify a set of illumination conditions that would optimize the ability to distinguish individuals with normal color vision and those with acquired defects resulting from early stages of retinal disease. For this purpose, we have documented the interaction of age and illumination level on the performance of the FM 100-hue test on a normal population. Third, we have collected normative data on the effect of aging on the TNO-tritan test, a quich test for tritan type defects.